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Roller Clutch
From WikiPedalia
A roller clutch (or "silent clutch" in Shimano terminology) is a type of freewheel ratchet mechanism which uses cams and rollers instead of pawls. It has been used in some cassettes and internal-gear hubs, notably in the Shimano Nexus and Alfine series.
In addition to eliminating the annoying "tick-tick-tick" of a pawl-type freewheel, a roller clutch has less slop when drive force is applied to it...drive begins as soon as forward motion of the pedals starts, unlike with a pawl-type freewheel which drives only once it has rotated far enough to let the pawls engage the notches of the ratchet ring.
